CO2, H2S, and other sulfur contaminants such as mercaptans and organic sulfurs are routinely removed from various gas streams in many conventional gas treatment configurations. Unfortunately, while most of these configurations remove the acid gases and sulfur contaminants to some degree, they are relatively ineffective in treating highly contaminated off-gases, and particularly refinery off gases that contain significant quantities of heavy hydrocarbons, oxygenates (e.g., carbon monoxide and sulfur dioxides), nitrogen compounds (e.g., cyanides and ammonium compounds), unsaturated hydrocarbons (e.g., olefins, dienes), mercaptans and other organic sulfurous compounds (e.g., methyl mercaptan, ethyl mercaptan, butyl mercaptan, carbonyl sulfide, dimethyl disulfide, carbon disulfide, propanethiol, thiophene, etc.). Therefore, gas treated in such known configurations frequently still contains unacceptable levels of sulfur contaminants (e.g., greater than 50 ppmv) and so fails to meet current environmental regulations. In addition, off gases from catalytic cracking units and other sources contain significant amounts of unsaturated olefinic compounds that often foul the combustion equipment and create unwanted emissions when used as fuel gas.
Chemical solvents such as amines and caustic are often ineffective in removing the heavy mercaptans and organic sulfurs (e.g., propyl mercaptans and DMDS). While physical solvents can absorb these contaminants, they tend to co-absorb excessive amounts of hydrocarbons that are then problematic in downstream processing units such as the sulfur plants. Additionally, many unsaturated olefinic hydrocarbons (e.g., propyldienes, butadienes) are reactive components that tend to polymerize and foul the processing equipment. Still further, relatively high levels of heavy hydrocarbons and mercaptans in the acid gases tend to create operational instability in a sulfur plant and typically require a high flame temperature in the Claus reaction furnace for destruction, which significantly reduces the life of the sulfur plant.
To circumvent at least some of the problems associated with inadequate contaminant removal, various pre- and post treatment methods have been employed. Unfortunately, most of such methods tend to be relatively ineffective and costly, and where contaminants are removed by a fixed bed absorbent, they may further pose a disposal problem for the spent absorbent. Even with pre- and/or post treatment methods, the quality of the acid gas produced in such treatment facilities is often poor and the treated gas still contains significant amounts of the undesirable sulfur and olefinic and aromatic hydrocarbon components, which cannot meet fuel gas specifications and therefore cannot be utilized as fuel gas.
In yet other known processes, and especially hydroprocessing operations during which mercaptans are catalytic converted to H2S, olefinic and aromatic hydrocarbons (e.g., ethylene, propylene, propyldienes, butenes, butadienes, benzene, toluene and heavy olefins) are reactive with other undesirable compounds that will invariably result in fouling of the heat exchangers and reactors and often result in a shutdown of the facility. Moreover, residual olefinic hydrocarbons in fuel gas will also result in undesirable side reactions and emissions in the conversion, combustion or power generation process.
Therefore, while various gas processing treatments and configurations are known in the art, all or almost all of them suffer from one or more disadvantages, and especially where the feed gas comprises relatively high levels of acid gases, olefinic and aromatic hydrocarbons, heavy mercaptans and/or organic sulfurs contaminants.